It is known that fluorine can be exchanged for chlorine, bromine or iodine bonded to phosphorus by reaction of the halophosphorus compound with a metal fluoride. The transhalogenation reaction is quite slow and difficult to push to completion. It is sometimes desirable to replace chlorine, bromine, or iodine bonded to phosphorus with a fluorine atom. For example, L. P. J. Burton U.S. Pat. No. 4,912,155, describes a family of aryl fluorophosphites that are very effective stabilizers in polyolefins, especially in combination with phenolic antioxidants, and are also hydrolytically stable. These compounds are made by first forming an aryl chlorophosphite by reaction of an appropriate aromatic hydroxy compound with PCl.sub.3 to form an aryl mono or dichlorophosphite and then transhalogenating the chlorine atom with fluorine by reaction with a metal fluoride such as potassium fluoride.
L. P. J. Burton and M. S. Ao, in U.S. Pat. No. 5,061,818, disclose that the transhalogenation of a chlorine, bromine or iodine atom bonded directly to phosphorus by reaction with a fluoride salt can be sharply promoted by including in the reaction mixture a hydrogen halide salt of a pyridine-type compound.
In U.S. Pat. No. 4,929,745, there is disclosed a method for exchanging a halogen bonded to a phosphorus compound having a halogen selected from chlorine, bromine or iodine bonded directly to phosphorus using a hydrogen fluoride salt of a pyridine-type compound such as pyridine hydrofluoride as the source of the fluorine.